1. Field of the Invention
The present invention relates to air defense systems, and more particularly pertains to a single unified system that may detect, track and even destroy airborne objects, even objects designed to move relatively undetected through conventional radar systems.
2. Description of the Prior Art
Radar systems using radio frequency waves are well known for detecting and tracking objects in the atmosphere of the Earth for the purpose of air defense. Such systems are used for guiding manned aircraft and unmanned weapon systems to the objects, and for destruction of the objects, if necessary. Thus, the conventional air defense systems have typically employed one system for detecting and tracking objects in the atmosphere, and a relatively separate system for destroying, or otherwise rendering ineffective, objects representing a threat to the protected ground area below the area of atmosphere being patrolled.
Technology has been developed that employs relatively higher frequency, shorter wavelength waves in the ultraviolet, visible, and infrared region of the electromagnetic spectrum are sometimes referred to as xe2x80x9clidarxe2x80x9d systems, which stands for xe2x80x9cLIght Detection And Rangingxe2x80x9d or xe2x80x9cLaser Infrared raDARxe2x80x9d, depending upon the particular source consulted. The lidar systems transmit and receive relatively short frequency electromagnetic radiation.
The basic instruments of a lidar system are a transmitter, a receiver, and a detector. A lidar system""s transmitter is typically a laser-generating apparatus, while the receiver typically includes optical equipment, in contrast to the radio wave transmitters and receivers of radar systems. Different types of lasers can be employed for the transmitter, depending upon the power and wavelength of the electromagnetic wave employed in the lidar system. Laser emissions are produced when high-voltage electricity causes a quartz flash tube to emit an intense burst of light, exciting some of the atoms in a ruby crystal to higher energy levels. At a specific energy level, some atoms emit particles of light called photons. At first, the photons are emitted in all directions. Photons from one atom stimulate emission of photons from other atoms and the light intensity is rapidly amplified. Mirrors at each end reflect the photons back and forth, continuing this process of stimulated emission and amplification. The photons leave through the partially silvered mirror at one end, and these photons comprise the laser light emission. An important fact to note is that the photons are energy. Therefore, when two laser beams are crossed, most of the photons will pass through the intersecting beam and continue on the same course as before they crossed.
The receiver of a lidar system detects the light waves scattered back to the receiver by objects in the path of the photons of the laser emission from the laser of the transmitter. The receiver records the scattered light received by the receiver at fixed time intervals. Lidar systems typically use sensitive detectors called photomultiplier tubes to detect the back-scattered light waves. The photomultiplier tubes initially convert the individual quanta of light, or photons, received by the receiver into electric currents, and then convert the electrical currents into digital photocounts that can be stored and processed on a computer. The electric currents generated by the receivers are normally in the range of picoamps.
The photocounts received by the receiver can be recorded for fixed time intervals during the return pulse of photons. The times can be converted to vertical heights above the ground, referred to as range bins, because the speed of light is a known constant. A range bin can be determined from a return pulse time. Range-gated photocounts (e.g., those photocounts that lie within a small range interval) can be stored and analyzed by a computer.
So far, the primary uses of lidar systems have been for detection of weather phenomena and pollutants in the atmosphere. The National Aeronautics and Space Administration (NASA) has also used a lidar system to map the topography of Mars. The military applications of lidar systems have included using them as range-finders to determine the distance to a target, and for missile defense. In a test in June 2000, the U.S. Air Force trained a high energy lidar laser on a missile for several seconds while tracking it with radar, and destroyed it in mid-air.
The four basic types of lidar systems are used primarily to measure pollutants in the air and to measure wind conditions. The types of lidar systems are similar in that all of the systems use lasers for transmitters and telescopes for receivers. However, each type of lidar system employs a different kind of light scattering.
One type of lidar system, the DIAL system, which stands for DIfferential Absorption Lidar, aims a laser at high and low regions of the atmosphere to measure the amount of ozone. Because light is absorbed at different wavelengths at different altitudes, a measurement of the difference in absorption of light can determine the amount of ozone present.
Another type of lidar system, the LITE system, which stands for LIdar Technology Experiment, is used to detect clouds and aerosols from space. It was used for the first time on NASA shuttle mission STS-64 in September 1994. The LITE system uses elastic scattering of light to measure aerosol particles in clouds. Elastic scattering means that the scattered light waves are at the same frequency as the incident light waves from the laser of the transmitter.
Yet another lidar system, the GALE system, which stands for Giant Aperture Lidar Experiment, measures wind, temperature and ocean waves using resonance fluorescence scattering. When sodium atoms in the atmosphere are illuminated by lidar laser emitted light waves at a precise wavelength, the sodium atoms radiate light waves that are measurable by receivers. By slightly changing the wavelength of the transmitted light, the shift of the spectral line from. its central wavelength can be measured. The shift of the central wavelength is known as the Doppler shift. The Doppler shift can be used to measure wind speeds and currents that could be important for airplanes trying to avoid turbulent winds.
Still another lidar system, the PCL, or Purple Crow Lidar, system measures temperature, waves and water vapor. The PCL system measures temperature with the same kind of sodium resonance-fluorescence scattering as in the GALE system. It also uses Rayleigh scattering from air molecules to measure temperature. Rayleigh scattering refers to the fact that different kinds of light scatter more strongly than others do. Blue light, for example, scatters five times more strongly than red light. The amount and color of the scattering depends on the kinds of molecules the light strikes. Oxygen, for example, produces significant scattering of blue light, which explains the blue sky of Earth""s atmosphere. The PCL system employs a receiver called a liquid mirror telescope. The liquid mirror telescope contains mercury or gallium that is spun to achieve a parabolic surface that can be used for lidar light wave measurement.
One prior use of lidar systems was NASA""s Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS). MACAWS is an experimental design that uses an airborne, pulsed, scanning, coherent Doppler lidar that remotely senses the distribution of wind velocity and aerosol back-scatter within three-dimensional volumes in the troposphere and lower stratosphere. The MACAWS components included a frequency stable, pulsed, transverse-excited, atmospheric pressure (TEA) CO2 laser transmitter producing 0.6-1.0 Joules per pulse between 9 to 11 microns (nominally 10.6 microns and 0.7 J) at a pulse repetition frequency (PRF) of 1 to 30 Hz (nominally 20 Hz); a coherent receiver employing a cryogenically-cooled HgCdTe infrared detector; a 0.3 m off-axis paraboloidal telescope shared by the transmitter and receiver in a monostatic configuration, a ruggedized optical table and support structure, a scanner, a data processing means, a real-time display, a storage device, and an Operations Control System (OCS) to orchestrate the operation of all components.
In the MACAWS experiment, five DC-8 airplanes were used simultaneously, each carrying a separate lidar system. Each lidar system was aimed through a window of the aircraft and created a scan plane that intersected with the scan planes of the other aircraft. The crossing of the laser emissions of the transmitters did not significantly deflect the trajectory of the photons of the laser emissions. Instead, the photons, which are energy, passed through each other and continued in straight lines. The goal of the experiment was to create holographic images of atmospheric conditions.
The first trial measurements were made Sep. 13-26, 1995 over the western United States and eastern Pacific Ocean. On May 24, 1996, another MACAWS flight measured wind speeds over central California. From Aug. 10-Sep. 22, 1998, MACAWS flights were used to obtain holographic dataxe2x80x94such as the velocity gradients and eyewall curvaturexe2x80x94on hurricanes Bonnie, Danielle, Earl, and George in the Atlantic Ocean.
The military usages of both lidar systems and lasers have included range finding. As range finders, the U.S. Army has used lidar systems on battlefields to determine the distance to a target, such as an enemy tank. In a range finder application, a laser transmits a pulse while a receiver (often little more than a lens) registers a pulse when back-scattered light is picked up by the receiver. A computer portion of the system measures the time interval between the time when the laser pulse is emitted and the reflected pulse is sensed. Because the speed of light is known, a measurement of the round-trip distance between the laser pulse and the receiver indicates distance to target.
More sophisticated lidar systems operate on substantially the same principle as the range finder. By adding multiple receivers at different locations and triangulating the results, the target can be accurately located in three dimensions, or holographically.
Alternatively, by adding a scan mirror to the laser transmitter, the beam can be directed to various parts of the target. By determining the small differences in distance to the target, the surface contours can be determined. Currently, this technique is used to look at the gross features of large objects. Similar information can be determined by replacing the receiver with an array of detectors.
NASA has employed technology similar to the range finder lidar system to map the topography of Mars using an orbiting satellite. The satellite directed a laser at the surface of Mars. Depending on the length of time it took for each pulse to create backscattered light, the lidar system could determine the heights of mountains, depth of valleys and other surface features of the planet.
Most of the other military applications of lasers involve shooting down missiles. An example occurred during a Jun. 7, 2000 test at White Sands Missile Range, N.M., in which the U.S. Army used its Tactical High Energy Laser/Advanced Concept Technology Demonstrator (THEL/ACTD) to shoot down a rocket carrying a live warhead. The test demonstrated the first high-energy laser weapon system designed for operational use. After the rocket was launched, a fire control radar detected the rocket, tracked it with its high-precision pointer tracker system, and then engaged the rocket with its high-energy chemical laser. After several seconds of having the laser beam directed on the warhead, the rocket exploded in mid-air. Although the system was originally designed as a stationary device, its primary subsystems have been packaged in transportable, semi-trailer-sized shipping containers, allowing it to be deployed to other operational locations.
The U.S. Army and Air Force also have been testing a similar airborne system. The lasers would be carried by airplanes that would direct the beams at incoming missiles to destroy them, similar to the Jun. 7, 2000 test at White Sands Missile Range.
The present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of providing a single unified system that may detect, track and even destroy airborne objects, even objects designed to move relatively undetected through conventional radar systems.
In view of the foregoing limited uses of lidars present in the known and prior art, the present invention provides a new apparatus and method for detecting, tracking, and destroying airborne craft, especially stealth-type aircraft designed to avoid detection by conventional radar, missiles and laser-guided bombs and missiles. It should be noted that none of the aforementioned DIAL, LITE, GALE, and PCL lidar systems has been used for military applications such as detecting and/or destroying aircraft, laser-guided xe2x80x9csmartxe2x80x9d bombs or missiles. In addition, all of the aforementioned systems use relatively low-energy lasers. The known systems could not be used to destroy or knock incoming aircraft, bombs or missiles off target. Finally, all of the lidar systems used for weather and atmospheric measurement have used no more than five laser transmitters at one time, and those transmitters were positioned at widely separated locations and aimed generally toward the other transmitters.
The general purpose of the present invention, which will be described subsequently in greater detail, is to diminish the risk of military or terrorist attacks that could be accomplished through stealth aircraft, missiles and laser-guided bombs and missiles.
To attain this, the present invention generally comprises a support, and a plurality of laser transmitters mounted on the support. Each of the laser transmitters are adapted to transmit a coherent beam of light along an axis, with the plurality of laser transmitters being oriented such that the axes of the beams of light emitted from the laser transmitters radiate outwardly from the support in sets of different angles to generate a grid of laser beams in the atmosphere. The system also includes a plurality of laser receivers and a processor for processing information from the laser transmitters and laser receivers.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.